Firstly the term frost-free only applies to freezers or the freezer section of a fridge/freezer. What it basically means is that ice should not form around your food and should never need defrosting. This is achieved by a fan circulating the cold air rather than the shelves themselves freezing. The 'freezing' is actually taking place behind the cover at the rear of the inside of the freezer compartment. The ice is defrosted periodically by a heater switched on and off by a timer, any excess water is than chanelled out via a tube to the tray on top of the compressor, where it evaporates.